Device for rolling threads

ABSTRACT

The invention relates to a device for introducing a thread into a workpiece having a cylindrical outer surface by means of thread rolling, comprising a profiling tool ( 7 ) having a profile without pitch, wherein the axis of the profiling tool is at an angle or parallel to the axis of the workpiece, wherein the profiling tool ( 7 ) is formed by a circular disk ( 9 ) rotatably mounted about the axis ( 8 ) of the disk, on the outer edge of which disk two annular, coaxial profiles ( 10 ) without pitch protrude, wherein said profiles form an annular space therebetween that corresponds in shape and dimensions to the thread profile of the thread to be created.

The invention relates to an apparatus for forming a screwthread in a workpiece having a cylindrical outer surface by screwthread rolling, comprising a profiling tool with a pitchless profile and having in particular a rotation axis oblique to an axis of the workpiece.

The term “screwthread rolling” refers in general to the noncutting production of a screwthread by cold working in which the profile is rolled into the surface of the corresponding tube section. According to DIN 8580, screwthread rolling falls under working, more specifically, compressive working, and within this, under rolling. Working is based on generating compressive stresses by means of one or more forming tools in the workpiece. This method is significantly faster and more cost-effective with high-volume production runs than are other methods for producing screwthreads—specifically, screwthread cutting.

The advantages of screwthread rolling thus include:

-   -   No grain boundary disruption as occurs with cutting;     -   Surface hardening is achieved by cold working;     -   Press-finished screwthread flanks can be produced;

An enhanced resistance to wear results;

-   -   Reduced notch sensitivity;     -   No swarf, and therefore reduced material requirement;     -   Lower effort required than with screwthread cutting

In conventional screwthread rolling using flat tools, the pair of jaws has the counter-profile with the pitch angle of the screwthread, one jaw being fixed while the other is movable. The workpiece is rolled along under the action of friction so as to create the screwthread around the entire circumference of the screwthread. The rolling jaws have sloped entry and exit sides, as well as a straight calibration section.

Screwthread rolling with circular tools can be performed using the infeed or throughfeed method. Either short or long screwthreads can be rolled even up to the head. In the infeed method, the rollers have a corresponding screwthread profile with the same pitch angle, however, with the opposite direction of twist. The workpiece is held either by a straightedge (centerless) or between centers. During the rolling procedure, the workpiece does not move axially except for slight compensating movements. Since the ratio of roller diameter to workpiece diameter and the number of starts must matched precisely to each other, a pair of rollers can be employed only for a very specific screwthread.

In the throughfeed method, the rollers have adjacent pitchless screwthread profiles. They are pivoted about their horizontal longitudinal axis to the required pitch angle. As a result, the axial feed of the workpiece is generated by the amount of the pitch during one revolution. To a limited degree, the rollers can also be employed for different workpiece diameters. However, this method results in reduced pitch accuracy as compared with the infeed method.

Self-opening screwthread rolling heads typically have three rollers. They are moved axially onto the workpiece and pull themselves automatically onto the workpiece through the oblique orientation of the rollers. Once the intended screwthread length has been reached, the roller head opens automatically and can be retracted.

The known screwthread-rolling apparatuses are always stationary since they are of considerable outside dimensions and great weight. An electrical drive is always required. Also inherent in the prior art in the area of screwthread rolling is the fact that they are implemented comprising rollers as well as machinery. The process of effecting an intended screwthread change necessarily means that multiple tools, preferably rollers, have to be replaced and that a machine-type drive must be provided.

The object of this invention is to create an apparatus for rolling external screwthreads that has maximum portability and is relatively simple to operate manually, while also being of simple design and small outside dimensions.

This object is achieved according to the invention in that the profiling tool is a circular disk (9) that is rotatably supported about its rotation axis and that has two annular, coaxial pitchless profiles projecting from an outer periphery of the disk and together defining an annular groove whose shape and dimensions correspond to the screwthread profile of the screwthread to be created.

The invention relates to an apparatus for rolling screwthread in which a workpiece is secured between rolling tool and clamping apparatus, and is clamped in place by a screw feed. After locking in place is completed, a screwthread can now be rolled into the workpiece by rotation by hand. The screwthread geometry of the workpiece is defined here by the rolling tool. The rolling tool preferably has a quick-change insert and as a result can within limits produce any desired external screwthread.

Along with simple construction, an apparatus of this type is sufficiently compact that it can be carried and operated by hand. It does not require an electrical drive; instead, forces can be generated by muscle power. Workpieces do not need to be moved to the screwthread-rolling apparatus; instead, the apparatus can be easily carried to the location where the screwthread is to be created.

In addition, the approach is not known in the prior art whereby the workpiece is supported as a smooth bearing since a freshly rolled screwthread could be damaged thereby depending on the level of expertise of the average person skilled in the art. On the contrary, a person skilled in the art will deliberately attempt to avoid this type of plain bearing so as to avoid any damage to the screwthread.

The solution according to the invention enables the work-hardening of the material due to the rolling procedure being used. Thus a combination of the working process in the form of screwthread rolling, together with the sizing and material selection of the feed adjustment apparatus, enable a standardized screwthread to be produced on a workpiece. In fact, cut screwthreads in the case of an axial “plain-bearing feed” here would be negatively affected to a relatively greater degree. The geometry and, depending on the material, the stresses on the workpiece are thus minimized.

Use on inaccessible workpieces (inside a machine that can be disassembled only a significant cost) is also rendered possible by this invention.

A more secure hold together with the simplest production is provided if the cylindrical workpiece is held in a part-cylindrical groove of a brace block, the longitudinal axis of which extend obliquely to the rotation axis of the profiling tool. The brace block here can be adjustable, in particular by hand, transversely, and in particular, perpendicular to the rotation axis of the profiling tool.

An advantageous alternative brace block for the workpiece is provided when the inside wall of the part-cylindrical groove includes a partial screwthread formation that essentially corresponds in shape and pitch to the screwthread to be created on the workpiece.

In addition, the cylindrical workpiece is supported on the side opposite the profiling tool by at least two rollers that are axially parallel to the workpiece and that are mounted in a brace block.

Simple and effortless manipulation is provided by the fact that the brace block can be operated by a threaded rod, in particular by hand, in order to adjust the spacing between the profiling tool and the brace block.

Preferably, an approach is proposed whereby the workpiece is able to be axially and/or radially insertable into and removable from the intermediate space between the profiling tool and the brace block. An especially advantageous aspect is that the screwthread-rolling apparatus as a hand tool is able to be operated by hand and is portable.

Perspective views showing embodiments of the invention are provided in the drawings and will be described in more detail below. Therein:

FIG. 1 shows a first embodiment in which the workpiece is held against the profiling tool in a groove of a brace block;

FIG. 2 shows a second embodiment in which the workpiece is held against the profiling tool by two rollers;

FIG. 3 shows an embodiment comprising a closed annular frame.

The screwthread-rolling apparatus 1 has a U-shaped frame 2 formed by a base 3 from which two arms 4 and 5 extend. The inner arm 4 has two arm halves 4 a and 4 b that form with a longitudinal slot 6 in which a profiling tool 7 is supported for rotation on a pivot 8 whose ends pass through both arm halves 4 a and 4 b so as to be held by the arm 4.

The profiling tool has circular disks 9 whose outer circularly annular, coaxial, and spaced peripheries 10 are of identical diameter and identical cross-section such that they form a coaxial annular groove 11 whose cross-section corresponds in shape and dimension to the cross-section of the profile of the screwthread to be generated. The dimensions and cross-section of the peripheries 10 are selected so as to correspond to the dimensions and the cross-section of the screwthread to be created.

A brace block 20 provided to press the cylindrical outer surface of the rod-shaped workpiece against the profiling tool is formed with a part-cylindrical groove 12 in which the workpiece lies and whose concave surface is shaped complementary to the screwthread to be generated. A threaded rod 12 [Translator's note: 13] supported on brace block 20 on the side opposite groove 12 is engaged in a complementary threaded hole of the outer arm 5 and can be rotated by hand about its longitudinal axis by a grip 14 at the rod's outer end so as to move the brace block 20 toward and away from the profiling tool.

Instead having the profiling tool 7 supported in the inner arm, it can also be supported in the block 20 while the inner arm 4 creates the counter-support and has the groove 12. In addition, the brace block 20 can as shown in FIG. 2 hold two guide wheels or guide rollers 21 that engage with profiled formations in the screwthread of the workpiece. Alternatively, the surfaces of the rollers 21 can be cylindrical and smooth, in particular when the screwthread is being repaired.

In addition, it is also possible for the frame 2 to be closed rather than U-shaped, i.e. the two arms 4, 5 are over-pressed [Translator's note: bridged] by a top piece 2 a such that the frame 2 is annular, with the brace block 20 located within its central opening as shown in FIG. 3.

In all embodiments, the pivot 8 of the disk 9, and thus of the two profiles 10 as well, defines an axis that is oblique to the axis of the groove 12, or relative to the guide edges 21 so as to enable a screwthread with a continuous screwthread turn, rather than simply annular grooves, to be created in the workpiece. The angle of this oblique orientation here measures 0.4° to 10°. The oblique orientation can be eliminated for the purpose of repairing a damaged screwthread, i.e., then the guide, in particular, the groove 12 in the brace block or guide piece 20 is parallel to the rotation axis 8 of the profiling tool.

The advantage of using the tool according to the invention without a machine is the fact that it is not tied to one location, can be flexibly employed, and, for example, set-up times are eliminated. The tool is thus appropriate for producing small quantities and is also significantly more cost-effective to produce than, for example a rolling head, since it is composed of a few simple parts.

This is enabled by the fact that disposed opposite a brace element only one single profile roller is used for forming. In known tools, the profile rollers have either a profile with pitch or a profile without pitch in the form of circular circumferential ribs or rings. A pitchless profile is also employed in this invention for forming; however, this profile is distinguished by the fact that it has only two circumferential ribs or rings that form an annular intermediate groove between them, which groove approximately corresponds to the screwthread profile to be shaped. Although it could in fact also have multiple rings, nevertheless when used only two engage the workpiece.

What this shape of the profile roller (only two circumferential rings or ribs engaged with the defined intermediate space) achieves is that it minimizes the force that must be applied to allow the profile roller to penetrate the material. In addition, the oblique orientation of this profile roller relative to the workpiece axis by approximately the pitch of the screwthread means that a complex restricted guidance, such as that found in known tools, can be eliminated, yet the profile roller nevertheless rolls a profile into the workpiece with precisely the desired pitch.

In order to apply the force needed to introduce the profile roller into the workpiece, the workpiece is supported by a brace element on the side opposite the profile roller. This can be, for example in the form of a solid body having a negative profile matched to the screwthread. A relevant factor for the brace element is that it transmit the force to the workpiece with the most extensive possible contact, not contact at intermittent points.

An advantageous embodiment of the tool resembles that of a pipe cutter, which differs from the above-described invention in that a level-oriented cutter wheel is employed instead of a profile roller that is oriented obliquely and imparts a profile.

The proposed embodiment of the tool is distinguished by the fact it is designed as a mobile portable hand tool. The profiling tool and the brace element here are able to be tangentially feed-adjusted relative to each other. At least one rest position can be set here at which a workpiece can be inserted between the profiling tool and the brace element. The ability to allow the workpiece to be inserted both axially as well as tangentially provides the greatest possible flexibility. In addition, the tool can form screwthreads not only at the end of a workpiece but at any point desired. A critical factor is that the profiling tool and the brace element lie in one force flow plane so that no bending or tilting moments are produced by a locking action on the workpiece to be worked. The tool is designed here such that the profiling tool is oriented obliquely at an angle relative to the workpiece axis, which angle approximately corresponds to the screwthread pitch.

In addition, possible feed adjustment allows the tool not only to be set at the end of the workpiece—instead, the screwthread can be rolled in a direction starting at the center of the workpiece up to the end of the workpiece. This prevents the tool from being set in an accidently skewed fashion. There is also no need to grasp the workpiece at the workpiece end—as is customary when cutting screwthread—so as to prevent a tilted or skewed application. At the same time, the advantageous properties of chip-free working using the apparatus according to the invention can be exploited, thereby allowing the advantages of screwthread generated by this type of method to be realized in mobile fashion by hand.

By surprisingly simple means here, after completion of the feed adjustment at a predetermined feed force in the working position by rotating the entire apparatus about the tool rotation axis, the external screwthread is introduced without swarf, where the screwthread geometry to be created is uniquely predefined by the profiling tool in terms of profile depth and profile shape. It is practically impossible to effect skewing or imprecise introduction of the profile. It is also impossible to effect an “excessively strong” feed adjustment since the forces increase exponentially as soon as the space between the two ribs or rings forming the profile have been completely filled in by the shaped workpiece. The geometry of the workpiece here requires only an essentially cylindrical outer surface, and can also be tubular or composed of a solid material. In addition, the external screwthread is formed completely up to a predefined point, thereby enabling a screwthread to be generated without runout. No electrical power supply is required here, with the result that a wide variety of possible applications is provided.

It is of course self-evident that other embodiments of the tool are conceivable in which the workpiece can only be inserted axially, but which can be implemented less powerfully since the forces can be more advantageously accommodated by the body of the tool.

Another possible application of the tool is screwthread repair. Deformed external screwthreads can be reshaped back to the original form using the tool. Due to the oblique orientation of the profile roller, relatively major damage can be repaired significantly more effectively than with the known tools. However, as was explained above, it is also possible to perform repairs of high quality on screwthreads even when the profile rollers are not oriented obliquely, i.e. when their axis is oriented parallel to the longitudinal axis of the workpiece.

Since the profile of the profiling tool and the angle by which the profiling tool is oriented relative to the workpiece axis are dependent on the type of screwthread to be generated, it is advantageous to design parts of the tools (the forming roller and the counter-holder) so as to be easily replaceable, thereby allowing the tool to be used to generate different screwthread types. This also makes sense since the counter-holder and the profile roller are subject to wear over time and can then be replaced. 

1. An apparatus for forming a screwthread in a workpiece having a cylindrical outer surface by screwthread rolling, the apparatus comprising a profiling tool with pitchless profile, wherein a rotation axis of the profiling tool is oriented obliquely or parallel to the axis of the workpiece, the profiling tool being a circular disk that is rotatably supported about its rotation axis and that has two annular, coaxial pitchless profiles projecting from an outer periphery of the disk and together defining an annular groove whose shape and dimensions correspond to the screwthread profile of the screwthread to be created.
 2. The apparatus according to claim 1, wherein the cylindrical workpiece is held in a part-cylindrical groove of a brace block, a longitudinal axis of the groove being oblique to the rotation axis of the profiling tool.
 3. The apparatus according to claim 2, wherein the brace block is adjustable transversely, in particular by hand perpendicular to the rotation axis of the profiling tool.
 4. The apparatus according to claim 2 wherein the inner wall of the part-cylindrical groove includes a partial screwthread formation that essentially corresponds in shape and pitch to the screwthread to be created.
 5. The apparatus according to claim 1, wherein the cylindrical workpiece is supported by at least two rollers that are axially parallel to the workpiece on the side opposite the profiling tool and that rollers are mounted on a brace block.
 6. The apparatus according to claim 2 wherein the brace block can be actuated by a threaded rod, in particular by hand, in order to adjust a spacing between the profiling tool and the brace block.
 7. The apparatus according to claim 1, wherein the workpiece is axially and/or radially insertable into and removable from a space between the profiling tool and the brace block.
 8. The apparatus according to claim 1, wherein the apparatus is a hand tool that can be operated by hand and is portable.
 9. An apparatus for forming an external screwthread in a cylindrical outer surface of a workpiece, the apparatus comprising: a frame having an inner arm and an outer arm spaced therefrom; a brace block on one of the arms formed with a part-cylindrical seat generally complementary to the workpiece outer surface and centered on a seat axis; a profiling disk centered on a rotation axis and having an outer periphery formed relative to the rotation axis with a pair of substantially identical, axially spaced, annular, and radially outwardly projecting ridges defining a radially outwardly open groove of a shape corresponding to a cross section of the external screwthread to be formed in the workpiece surface; a pivot rotatably supporting the disk on the other of the arms with the disk rotation axis extending nonparallel to the seat axis at a small acute angle corresponding to the pitch of the external screwthread to be formed in the workpiece; and means for displacing the brace block relative to the one arm toward the disk with a workpiece fitted in the seat such that the ridges engage into and plastically deform the workpiece outer surface and, on rotation of the workpiece relative to the frame, cold-work the external screwthread into the workpiece. 